Truck covers commonly called "caps" for pickup trucks and similar vehicles are commonly equipped with a rear door which cooperates with the tailgate to provide access to the interior of the top cover and the bed of the vehicle.
Such doors have been provided with various mechanisms, herein referred to as props or supports including spring-loaded telescopic cylinders, to support the door in an open position, and when closed, to assist in holding the door in a closed position. The support or prop is conventionally affixed by rivets or similar fastening means to the flat inside face of the metal framework of the door sash. Generally, the wall thickness of the door frame is not sufficient for the fastening means to withstand the forces on them without pulling loose and as a result, the door frame has conventionally been reinforced by a backing plate inserted behind the wall through a specially prepared opening cut into the side of the frame. Such backing plates involve additional costs and manufacturing steps as they require an opening to be cut through the side of the sash and the backing plate inserted between the front and back surfaces of the door sash to receive the rivets.
The telescopic prop, which may be a metal tubular spring-loaded structure, is fixed at its opposite end to the frame formed in the top. It is usually spring loaded to hold the door in an open position and the prop assumes an over-center position to hold the door closed. The amount of force applied by the spring within the prop to hold the door in open position is determined by its particular application and is selected by considering such parameters as door size and weight. The force applied must be sufficient to hold the door open and yet must not be so great such that excessive forces are applied to the door frame and sash when the door is moved to closed position. Usually in each such application, two props are installed, one on each side of the door. In one typical application, the props positioned at opposite sides of the door are equipped with props having a spring force of 18 pounds, this force conventionally referring to the spring force applied between the telescoped members when in compressed condition. Obviously, when expanded, the spring must provide sufficient force to hold the door in open position.
Heretofore, attempts have been made to reduce the gauge of the metal used in the door and to reduce the overall cross-sectional dimensions of the door frame in order to reduce the costs of the doors and provide a less expensive construction for the public. However, such attempts have compounded the problem of securing and fastening the prop to the door so as to withstand the lateral and twisting forces exerted on the securement and fastening means.
Attempts have also been made with respect to preexisting doors and even the lighter gauge doors to provide a door structure using only one prop positioned at one side of the door. In such constructions, the prop is subjected to even greater forces and stresses tending to cause the rivets or other fastening means by which the mounting bracket is fixed to the door sash to pull out of the metal resulting in damage to the door and great inconvenience to the owner. In such instances, even the conventional backing plate positioned inside the door sash did not provide sufficient reinforcement.